Experiment with restricting form submission with open elements.

third_party/WebKit/Source/core/html/HTMLFormControlElement.h

Index: third_party/WebKit/Source/core/html/HTMLFormControlElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLFormControlElement.h b/third_party/WebKit/Source/core/html/HTMLFormControlElement.h
index 3902398e620242a75274be44b44728421055daa4..308b7639a9d0240f31cef069ede000d98d0be2c3 100644
--- a/third_party/WebKit/Source/core/html/HTMLFormControlElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLFormControlElement.h
@@ -132,6 +132,9 @@ class CORE_EXPORT HTMLFormControlElement : public LabelableElement,
   FormAssociated* toFormAssociatedOrNull() override { return this; };
   void associateWith(HTMLFormElement*) override;
 
+  bool blocksFormSubmission() const { return m_blocksFormSubmission; }
+  void setBlocksFormSubmission(bool value) { m_blocksFormSubmission = value; }
+
  protected:
   HTMLFormControlElement(const QualifiedName& tagName, Document&);
 
@@ -207,6 +210,7 @@ class CORE_EXPORT HTMLFormControlElement : public LabelableElement,
   bool m_validityIsDirty : 1;
 
   bool m_wasFocusedByMouse : 1;
+  bool m_blocksFormSubmission : 1;
 };
 
 inline bool isHTMLFormControlElement(const Element& element) {